1. Field of the Invention
This invention relates to an open bearing rotary cone rock bits principally used in surface mines. In quarrying, the presence of liquid in the borehole is objectionable. Hence, open bearing, air-lubricated rock bits are utilized, especially since the normal depth of the borehole is only a few hundred feet.
More particularly, this invention relates to rotary cone air bits with an internal drip lubrication system to entrain lubricant along with compressed fluid or air directed to the bearings of the rotary cone rock bit.
2. Description of the Prior Art
There are many patents directed to the use of lubrication systems in both rotary cone sealed bearing rock bits that run in liquid or "mud" and open bearing rock bits that are cooled and lubricated by a fluid directed down a drillstem to the bit.
U.S. Pat. No. 2,751,196, issued to B. D. Smith, is directed to a lubrication system for a dry rock drilling bit. This invention is directed to an open bearing roller cone rock bit having a chamber in its upper portion for receiving compressed air and three cutter elements rotatably carried on the lower portion of the bit. The body also provides air passages that extend from the chamber adjacent the cutter elements, with ducts which extend from the chamber to the bearing passages formed between the cutter cones and their respective journals. A central cylinder extends into the chamber from a dome section of the bit body to receive air pressure from the chamber and outwardly to the borehole bottom. A reservoir is formed between the cylinder and the body in the chamber to receive liquid lubricant. The lubricant is directed to this reservoir down a drillstring and into the reservoir. The inner cylinder extends above the level of the liquid so that air is directed through the chamber and into the borehole bottom to remove detritus from the borehole bottom. The liquid lubricant is fed directly to the bearings between the cutters and the journals. Air pressure then forces lubricant into each of the respective bearings.
The present invention is an improvement over the foregoing patent in that it provides a lubricant reservoir in a chamber formed by the rock bit body. The reservoir feeds lubricant into the air passages, directed to bearings formed between the cutter cones, and their respective journals by directing a tube from the bottom of the oil reservoir into the top of the air passages communicating with the bearings of the rock bit. The oil is entrained by the air passing into the air cooling passages as the air is directed to the bearing area of the rock bit. The rock bit of the present invention thus receives the cooling effect of the fluid on air directed to the bearing passages, along with entrained oil that is dripped into the air passage as the bit works in a borehole--thus each of the roller cones on the bit are lubricated as well as cooled as the bit works in a borehole.
U.S. Pat. No. 3,924,695, issued to John R. Kennedy, discloses a rotary drill system for dry hole drilling with the use of an open bearing rotary cone rock bit. The system requires a fluid with oil entrained by the fluid and directed from the drilling rig down the drillstring into a chamber formed in the rotary cone rock bit. A separator is located centrally of the chamber within the rock bit body. The separator serves to separate the liquid entrained in the fluid from the air. The liquid essentially goes around a conically-shaped central device which allows air to enter the center of the separator body, the oil going outside of the body. The collected oil in the base of the chamber is directed to the bearings formed between the cone and the journal. The separated air then is directed through a nozzle in the bit body to the exterior of the bit to lift detritus material from the borehole bottom, up the outside of the drillstring and out of the borehole.
The instant invention has an advantage over this patent in that the fluid directed down the drillstring need not have entrained therein a lubricating constituent. By providing a reservoir of liquid that is dripped or entrained into the air bearing passages by compressed fluid, there is no necessity to entrain liquid into the compressed fluid at the rig platform. The air passing into the bearing passages for cooling purposes picks up oil dripped into the entrance to the air/lubricating passages, therefore carrying oil in measured amounts to the bearing surfaces while still providing the cooling effect of the fluid or air to the bearing areas associated with a rotary cone rock bit.
The present invention obviates the problems associated with both of the foregoing prior art patents in that it has the advantage of providing a source of lubricant within the rock bit itself while preserving the advantage of the air circulation system wherein air is directed through conduits that lead to the bearings formed between the rotary cones and their respective journals. The '196 patent essentially obviates the beneficial effect of the cooling air by filling all of the air bearing passages completely with liquid while the '695 patent requires that the pressurized fluid source at the top of the drilling rig be supplied with an oil constituent so that the oil is carried along with the compressed fluid as it is directed all the way down the drillstring into the drill bit.
Again, the instant invention has the advantage of the cooling air to the bearing surfaces along with a means to supply a measured amount of liquid lubricant to the bearings as the open bearing bit works in a borehole.